1. Field of the Invention
The present invention relates to an electroluminescence device and a functional device.
2. Description of the Related Art
Out of various display devices, electroluminescence devices, wherein a light emitting layer is sandwiched between a pair of electrodes and a voltage is applied to the electrodes across the electrodes so as to cause luminescence, exhibit high luminance and high response speed. Thus, attention has been paid to the devices and practical use of the devices has been advancing.
In order to produce an electroluminescence device, adopted is a method of laminating, on a substrate, an anode layer, a light emitting layer and a cathode layer successively. In order to form the light emitting layer actually, various layers which constitute the light emitting layer are successively laminated.
Out of the above-mentioned layers, electroconductive layers such as the anode and the cathode are preferably laminated by sputtering for the production efficiency thereof. However, the underlying layer of the cathode layer is the light emitting layer; therefore, when the cathode layer is laminated, the performance of the light emitting layer is easily deteriorated by the exposure of the light emitting layer to sputtering particles, which have a high energy, or to a plasma atmosphere if plasma is used.
Incidentally, about any electroluminescence device, the material which constitutes its light emitting layer is sensitive to a physical or chemical environment change so that a dark spot may be frequently generated. Accordingly, in order to prevent the invasion of water content in the air, which is a cause of the dark spot, the whole of the electroluminescence device may be covered with a protection film for blocking the water content (Japanese Patent Application Laid-Open (JP-A) No. 2003-338363).
Suggested is also a manner of laminating, on a substrate, an anode, a sputtering protection layer and a cathode layer successively wherein the sputtering protection layer is composed of gold, nickel or aluminum (JP-A No. 2003-77651).
It is suggested that a cathode of an organic electroluminescence device is composed, from the organic light emitting layer, of an electron injecting electrode layer (composed of Mg, Ca, Ba or the like) and an amorphous transparent electroconductive film (composed of an In—Zn—O oxide film). This structure results in the evasion of an inclination to the invasion of water content or oxygen in the air into the cathode, which is composed of ITO or the like (JP-A No. 10-162959).
Furthermore, the following are suggested: an electroluminescence device comprising a substrate, a lower electrode, an organic EL (electroluminescence) layer, a buffer layer and an upper electrode wherein the buffer layer comprises a phthalocyanine compound doped with metal such as Au, Pt, Pd or Ag (JP-A No. 2004-296234); and an electroluminescence device having an electron transportation protecting layer made of a mixture wherein an alkali metal or alkaline earth metal such as Li, Cs, Ba, Sr or Ca is incorporated into an electron transporting organic material such as BCP (bathocuproine) (JP-A No. 2004-127740).
JP-A No. 2003-338363 states that when the protection film made of a high melting metal is formed on the cathode, the protection film can be formed by sputtering since the cathode, which has already been formed, functions as a buffer layer. However, JP-A No. 2003-338363 never discloses any solution for a deterioration of the light emitting layer when the cathode is laminated.
JP-A No. 2003-77651 refers to a theme for overcoming a deterioration of the light emitting layer when the cathode is laminated. However, in the case of using the metal for the protection layer, the protecting function is more preferred as the thickness of the protection layer is larger. Conversely, however, the transparency becomes lower. It is therefore difficult to make the required protecting function and transparency compatible with each other.
According to JP-A No. 10-162959, at the time of forming the amorphous transparent electroconductive film on the electron injecting electrode layer by sputtering, the electron injecting layer, which is an underlying layer, may produce a protecting effect. However, if the electrode layer is made to have a thickness sufficient for exhibiting the protecting effect, a drawback that the transmittance declines is unavoidable.
JP-A No. 2004-296234 includes the restriction that metal-doped phthalocyanine is used, and JP-A No. 2004-127740 includes the restriction that alkali metal or alkaline earth metal doped BCP (bathocuproine) or the like is used; however, in the present invention, metal-doped phthalocyanine is not used. The work function of each of the metals used in JP-A No. 2004-127740, such as Li, Cs, Ba, Sr and Ca, is smaller than 3.0 eV; however, the work function of the metal used in the invention is 3.0 eV or more. Thus, the two are different from each other.